- Calculate the top speed of a model airplane

- Dimitrios Katsoulis
- February 5, 2017
- No Comments

How fast your airplane flies? If you don’t have a speed radar gun then here is a practical way to calculate it with the airplane firmly secured on the ground.

1. With the engine properly tuned, measure the engine’s revs using a digital tachometer.

2. Take a note of the propeller’s pitch. As an example note 12 inches.

3. Measure the propeller’s revolutions with the airplane’s engine at full speed. As an example note **6.750 revs/min.**

4. Multiply the above number of revolutions by the propeller’s pitch. i.e **6.750 x 12 = 81.000 (inches/min).**

5. Multiply **81.000 (inches) x 60 (minutes) = 4.860.000 (inches/hour).**

6. Divide by 2,54 (inch match to centimeter) **4.860.000/2,54= 1913 meters/min, **which is** 1,913 Km/min.**

7. Multiply by 60 (min): **1,913 x 60= 114,78 Km/hour.**** **

8. Multiply by the factor 0,95 (as note): **114,78 x 0,95 = 109,41 Km/hour.**

** **** **

* NOTE*

*The ground speed is multiplied by a factor of 0,95 which depends on the model’s frontal area and its configuration (low wing or upper wing) in order to calculate the model’s air speed.*